Each album needs to be organized for the sake of the adult keeping track of what is going on. This organization is not how to present to the children but aids the adult in personal organization.
The same curriculum is given at 9-12 as is given at 6-9. In terms of geography, history, music, art, in particular, but also all the subjects areas, all of the general areas of the work need to be introduced in the 6-9 group in some manner; however, every presentation will not be covered, and many of the details are not reached until 9-12, when the children are interested in those details. 6-9 is an introduction to and a preparation for the work at 9-12.
In a classroom setting, each group of children may be focused on different areas at a time; the adult will be presenting from different areas throughout each day. Sometimes, there is a logical sequence and build-up, with pre-requisites for some of the work; however the children do not simply proceed through one entire chapter before moving on to the next. “What do the children need to know before presenting something?” is the only consideration before allowing a child to pursue a personal interest.
For example, here are the chapters of geography:
1) The Story of God with No Hands and the Creation of the Universe
2) Nature of the Elements
3) The Sun and the Earth
4) The Work of Air
5) The Work of Water
6) Interdependencies and Economic Geography
The adult will present the Story of God with No Hands every year. Then different groups of children will go off to personal studies of interest, either in geography or perhaps they have another project they are working on. For the rest of the year, the adult might be presenting some things from chapter 2 to a particular child or group of children - maybe finish an album page, maybe not. Then move on to another chapter (not even necessarily in chapter order!).
There is work for 6 year olds and 12 years in every single chapter.
Mathematics is a bit more linear, however many album pages are still set-up to be multi-age. An album page on fractions includes many exercises that extend from 6 to 8 1/2, then it is expected that the child's work will continue into 9-12 integrated with the other subjects (ie that they will actually use fractions in their history, geography, language, etc) and review the material from time to time as suggested by the public school curriculum (local educational requirements).
In language, we expect to review all lower elementary concepts in upper elementary, in a different way if they have mastered all the material: perhaps informal conversations, expecting proper grammar and word syntax in their writing, reading grammar books as follow-ups. There are few specific activities for this follow-up, because some children just won't need it; and those that do, will present a wide variety of types of reviews needed. There is no one-size-fits-all here :)
Follow the child!
Get the children doing independent research and studies, Goings Out and applying what they are learning to real life.
Then you have an elementary Montessori experience!